I believe the reason why God absents himself in an apparent fashion from many Atheists purview is because Atheists have this attitude.Another thing I notice is that militant atheists tend to be tolerant of polytheism. Polytheism doesn't inflame them as much as monotheism, especially the way Christianity does. Back when this place was a game forum, there was this very prominent member named soup. He fit the standard atheist portfolio: lived in a major city, was fascinated with pop science, into liberal politics (minus the feminism) and absolutely detested Christianity and God. He once stated that even if he could be shown that God existed, he would still hate Him. Also, he talked about how if he was forced to follow some sort of religion his first choice would be to pick the Norse pantheon and that he would look to figures such as Odin and Thor for guidance since he saw them as much more masculine.
Sometimes you'll see these sort of people saying stuff like "Hail Odin" when someone around their vicinity mentions something related to Christianity. Obviously, this is supposed to be meant in mockery and not a statement that they are actually Norse pagans but I feel behavior like this is revealing of what they are sympathetic towards. I vaguely remember a Stephen Fry video where he was talking about even though he's an atheist, he found Greek gods to be more palpable to him than a monotheistic one. It's a general attitude I've seen around atheists that are hostile to faith: they don't believe in any sort of polytheistic gods but they still are fascinated by them and just find them to be more cool than God. For me, this is further illustration of how polytheism really is ultimately just an early form of humanism, the deification of man and of self-worship.
And God will not throw his Pearl before Swine.
So yes Atheists do get confirmed in their Atheism once they have consistently attempted to ignore God despite him reaching out to them in the 1st place.
1st like Pharoah. They harden their hearts(Exodus 8:32). Then God hardened their hearts in response to repeated hardenings of their heart(Exodus 9:12).
Therefore if their Atheism is crystalized. God has decided to make them a Vessel of Wrath to demonstrate his Justice.